1. Field of the Invention
The present invention relates to an emulsified composition. More specifically, it relates to an emulsified composition suitable for use as a preparation for parenteral administration.
2. Description of the Related Art
Various emulsified compositions have been used in the field of, for example, pharmaceutical preparations and quasi-drug. For example, a fat emulsion for intravenous injection, which is a dispersion of lipid spheres with an average particle size of about 0.2 .mu.m dispersed in an aqueous phase, is already known in the art. This emulsion is usually formed by emulsifying a vegetable oil with lecithin as the emulsifier, using a high pressure homogenizer, and is utilized for a nutrient supplementation of patients or as the preparation for a parenteral administration of a lipid-soluble drug. Particularly, it is effective as the preparation for an intravenous injection of a lipid-soluble drug, which usually cannot be intravenously injected as an aqueous solution, and is utilized as a drug delivery system.
Recently, passive or active oriented drug delivery systems using microspheres have been studied, it has been found that particles of 0.100 to 2.000 .mu.m, when administered intravenously, intraarterially or intraperitoneally, are rapidly taken in from the blood stream by macrophages of the reticuloendothelial system, to become localized in lysosomes of Kupffer cells of the liver, and that particles of 0.050 .mu.m or less are considered to permeate through the liver endothelial system and accumulate at tumor tissues (Pharmacy International 2 (3) 1984). From such a standpoint, the above lipid emulsion for an intravenous injection with an average particle size of 0.2 .mu.m, which has a particle size readily taken into the reticuloendothelial system, particularly the liver, is not satisfactory as the preparation for a parenteral administration of a lipid-soluble drug, and therefore, it is very important in pharmaceutical preparation to be able to prepare particles of 0.050 .mu.m or less which can be parenterally administered. The above-mentioned lipid emulsion for intravenous administration is known as an emulsion which can be parenterally administered, but in the system of this lipid emulsion, it is very difficult to prepare particles of 0.050 .mu.m or less which can be parenterally administered, namely nanolipid spheres, and thus further research must be made into this problem.